Optical modules, such as those used, in particular, in optical communications, comprise optical or optoelectronic components that are disposed on a support and are coupled to one or more optical fibres. The support, which is also described as board or submount, is frequently composed of silicon. To couple the optical fibre, there has been introduced into the support a groove into which the stripped fibre, i.e. the fibre freed of the outer coating, is laid and mounted.
There is a plurality of possibilities for fixing the fibre. The possibility most used is to fix the fibre in the groove with adhesive, generally an epoxy resin. For this purpose, the fibre is aligned in the groove in order to achieve maximum coupling and then fixed with the adhesive. In this process, it may happen that the coupling optimized previously by alignment deteriorates during the curing of the adhesive. The bonding process can at present not be satisfactorily monitored and this leads to deterioration of the optical properties and increase in rejects during production. On the other hand, the bonding point is a weak point in regard to reliability and service life of the optical modules. The adhesive is subject to an ageing process that is promoted by exposure to light. In addition, there is the desire for epoxy-free optical modules.
A further possibility for fixing the fibre on the support is to metallize the fibre and solder it on the support. For this purpose, the metallized fibre is either soldered into a small metal tube on the support or is firmly soldered between the metallized support and a cover plate. This approach is technically very involved and expensive. On the one hand, metallized fibres are very expensive. On the other hand, either a deeper groove has to be etched into the support for the small metal tube, which requires development and design of new supports, or a cover plate has to be provided, which increases the support's surface necessary for the purpose. Both have the result that the supports have to be of larger dimensions so that fewer supports can be produced from a wafer and, in addition, a larger casing is needed for the module. A further disadvantage in soldering fibres is mechanical robustness. Soldered fibres break easily at the edge of the support. Tests have shown that, during tensile loading, the fibres break off, as a rule, before they are pulled out.
From the article entitled “AlO Bonding: A Method of Joining Oxide Optical Components to Aluminum Coated Substrates” by A. Coucoulas et al, 1993, Proceedings of 43rd Electronic Components and Technology Conference, pp. 470-481, it is known, for fixing fairly small optical elements such as ball lenses and for fibres, to coat the elements with SiO2 and press them into an aluminium-coated recess on the support using a thermocompression method. This produces a cold weld between the SiO2 layer of the element and the aluminium coating of the support. For this purpose, a ball lens has to be pressed into a suitable aluminium-coated recess with an application pressure of up to 50 N. In this process, it forms a cold weld at a few contact points. Fibres are pressed into an aluminium-coated V-groove. Since they rest in the V-groove over its entire length, a substantially higher application pressure is needed than for ball lenses. In this process, there is the danger that the support is damaged or destroyed. If a lower application pressure is chosen in order not to damage the support and the fibre, the mechanical joint between fibre and aluminium coating is inadequate.